Some of pharmaceutical products, specimens, and the like used in medical facilities such as hospitals and the like and some of foods and the like available in supermarkets and the like need to be kept cold or warm within a certain temperature range during transportation so that their qualities are maintained.
As a method of keeping such articles (e.g., pharmaceutical products, specimens, foods, and the like) cold or warm, there has conventionally been known a method in which (i) a cold storage material or a heat storage material, which has been solidified or melted in advance, is placed in a transport container having a thermal insulation property and (ii) latent heat of the cold storage material or the heat storage material are utilized to keep the article cold or warm while the article is housed in the transport container.
In a case where an article, which is intended to be kept cold or warm (hereinafter, such an article may be referred to “temperature control target article”), is to be maintained within a certain temperature range (hereinafter, such a temperature range may be referred to “controlled temperature”) for a long period of time, it is necessary to use a cold storage material or a heat storage material which (i) has a melting point within the certain temperature range and (ii) has great latent heat of melting.
Among such cold storage materials, a cold storage material, in which a cooling medium is an inorganic material such as inorganic salt, inorganic hydrate, or the like has the following advantages compared to a cold storage material in which an organic material is used: (i) a quantity of latent heat of melting is larger, (ii) a thermal conductivity is greater, (iii) a volume change is smaller, (iv) nonflammability is greater, (v) and the like.
Meanwhile, in a case where an article such as a pharmaceutical product, a medical device, a specimen, an organ, a chemical substance, food, or the like is to be transported in a frozen state, it is sometimes necessary to maintain the article at a controlled temperature ranged from −75° C. to −40° C. Dry ice has conventionally been used as a cold storage material, and is inexpensive and versatile. However, dry ice is treated as a hazardous material so as to be limited in the amount to be used particularly in a case of air transportation, and the like. This is because dry ice expands in volume when sublimating.
Examples of a cold storage material that can be used in a low temperature range other than dry ice include a cold storage material obtained by mixing water and an organic solvent having a low melting point, such as acetone and the like. However, as described above, an organic material is inferior to an inorganic material in terms of (i) a quantity of latent heat of melting and (ii) heat conductivity. In addition, an organic material is flammable and is therefore a hazardous material in many cases. An organic material is therefore hardly a safe and effective cold storage material.
Meanwhile, there has also been disclosed a cold storage material in which an inorganic salt that produces a eutectic mixture with water within or near the low temperature range is used.
For example, Patent Literature 1 discloses a cold storage material composition having a melting point of −46.7° C. This cold storage material composition is obtained by mixing a calcium chloride as an inorganic salt with water in an amount of 30% by weight (6.4 mol %) relative to the water, and a eutectic point of the calcium chloride with water is −55° C.
Meanwhile, Patent Literature 2 discloses a cold storage material composition having a melting point of −47.5° C. This cold storage material composition is obtained by (i) mixing calcium chloride in water in an amount of 15% by weight (i.e., 1.3 mol % after mixing) and (ii) mixing magnesium chloride (whose eutectic point with water: −33.6° C.) in the water in an amount of 5% by weight (i.e., 0.5 mol % after mixing).